The Fragile, Invisible Connections Of The Natural WorldFrom the TED Radio Hour, writer and environmentalist George Monbiot tells the story of what happened when wolves were re-introduced to Yellowstone National Park after a 70-year absence.

Something unexpected happened in Yellowstone National Park in 1995. For years, deer had grazed large areas of the park's native vegetation to bare roots. Now that was because the deer had no natural predator. The gray wolf, once native to the park, had been all but hunted out 70 years earlier. But in 1995, Congress authorized a small effort to reintroduce gray wolves to the wild. From the TED Radio Hour, George Monbiot explains what happened when the wolves returned.

GEORGE MONBIOT: First, of course, they killed some of the deer, but that wasn't the major thing. Much more significantly, the deer started avoiding certain parts of the park, the places where they could be trapped most easily, particularly the valleys and the gorges. And immediately, those places started to regenerate. Bare valley sides quickly became forests of Aspen and Willow and Cottonwood. And as soon as that happened...

(SOUNDBITE OF BIRDS CHIRPING)

MONBIOT: ...the birds started moving in.

(SOUNDBITE OF BIRDS CHIRPING)

MONBIOT: The number of beavers started to increase because beavers like to eat the trees.

(SOUNDBITE OF WOOD CRUNCHING)

MONBIOT: And the dams they built in the rivers provided habitats for otters and muskrats and ducks and fish and reptiles and amphibians. The wolves killed coyotes, and as a result of that, the number of rabbits and mice began to rise, which meant more hawks, more weasels, more foxes. Ravens and bald eagles came down to feed on the carrion that the wolves had left. Bears fed on it too and their population began to rise as well. And the bears reinforced the impact of the wolves by killing some of the calves of the deer.

(SOUNDBITE OF BEAR GROWLING)

MONBIOT: But here's where it gets really interesting. The wolves changed the behavior of the rivers.

(SOUNDBITE OF WATER FLOWING)

MONBIOT: And the reason was that the regenerating forests stabilized the banks so that they collapsed less often so that the rivers narrowed, more pools formed, more ripple sections. All of which were great for wildlife habitats. The rivers changed in response to the wolves.

(SOUNDBITE OF WATER FLOWING)

MONBIOT: When you look at it like that, you think, wait a minute. Here are the wolves changing the physical geography of the Yellowstone National Park, this huge area of land. You begin to see that the natural world is even more fascinating and complex than we thought it was. They tell us that when you take away the large animals, you are left with a radically different ecosystem to one which retains its large animals. And they make, in my view, a powerful case for the reintroduction of missing species.

SIMON: More on the fragile, and sometimes invisible connections in the natural world this weekend on the TED Radio Hour. This is NPR News.

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